THE STAIRCASE PHENOMENON OR BOWDITCH EFFECT IN Drosophila melanogaster

PARONZINI HERNANDEZ NADIA; MATTIAZZI ALICIA; REGGE VICTORIA ; SANTALLA MANUELA; FERRERO PAOLA; BALCAZAR DARÍO; VALVERDE CA

Buenos Aires

Congreso; Reunión conjunta de sociedades biomédicas; 2017

SAFIS

Drosophila melanogaster is a genetic useful model for cardiac studies. However, heart D. melanogaster physiology is poorly understood and its characterization is a necessary and mandatory step to extrapolate results of mutagenesis of human conserved genes. The main goal of the present experiments is to characterize in D.melanogaster intact heart, a fundamental property of the heart: the staircase phenomenon. Staircase phenomenon establishes the relationship between heart rate (HR) and contractile force: an increase in HR, progressively increases the force of contraction. This physiological response is important during exercise and it isobserved in healthy individuals and big mammals. Instead, negative staircase occurs in human heart failure, small mammals and other vertebrates. To determine the nature of the staircase phenomenon in D. melanogasterwe measured mechanical activity and Ca2+ transient of adult flies exposed to three 0.5 Hz increments of stimulation frequency (F1 to F3) over the basal spontaneous HR in semi-intact preparation.Although results of movement recordings were somewhat variable, in average, the increment in frequency did not produce significant changes in mechanical activity (Basal: 100% n= 9, F1: 103.8±8.03 n=9, F2: 95.3±9.5 n= 7, F3 105.7±23.9 n=4). In contrast, Ca2+ transient exhibits a clear significant negative staircase (basal:100% n= 5, F1: 73.0 ± 6.4 n=4, F2: 62.2±7.4 n= 5, F3 42.7±8.6 n=5, ANOVA analysis), as it is indicated by the tight relationship between peak Ca2+ transient decrease and HR increase (correlation coefficientof Pearson R2 = 0.89). Conclusion: 1. D. melanogaster has not a positive staircase phenomenon. 2. The uncoupling between the decrease in Ca2+ transient and the absence of significant changes in movement, might suggest an increase in myofilaments Ca2+ sensitivity. Further experiments are required to confirm this possibility andto study the possible mechanisms involved.Keywords: Bowditch effect, Contractility, Calcium, Drosophila melanogaster.